1. Field of the Invention
The present invention relates to a colorful liquid crystal on silicon (LCoS) display, and more particularly, to a reflective color LCoS display.
2. Description of the Prior Art
LCoS display technology is the key of reflective LCoS projectors and rear-projection televisions. The advantages of LCoS micro-displays are a tiny size, high resolution, low power, low cost, etc. The difference between an LCoS display and a conventional thin film transistor-liquid crystal display (TFT-LCD) is materials used for forming the substrates. Both a cover substrate and a backplane are made of glass in a TFT-LCD. Nevertheless, the cover substrate in an LCoS display is made of glass, but the backplane in an LCoS display is a semiconductor substrate, such as silicon. Therefore, an LCoS process combines LCD techniques and complementary metal-oxide semiconductor (CMOS) fabrication processes.
The main structure of an LCoS display includes a light source module, an LCoS panel, and a color separation and combination optical system. Generally speaking, the LCoS display can be divided into three-panel LCoS displays and single-panel LCoS displays according to the type of optical engine. The three-panel type optical engine separates lights generated from light source into red, blue, and green lights through a plurality of prisms, projects those lights into three separated LCoS panels respectively, and combines those three lights from each LCoS panel to form colored images. The single-panel type optical engine utilizes a color wheel to form red, blue, and green lights sequentially from white lights, and synchronizes the three kinds of lights with single-colored images, the red, blue, and green images, formed by driving programs so as to produce color-separated images sequentially. Since human eyes have the persistence of vision, people can see colored images from the projected images.
As a result, in the conventional LCoS displays, it is rare that a LCoS panel has a color pixel array with different types color filter layers because the fabrication technology of the micro color filters formed with inorganic dichroic materials is difficult and has high cost. Therefore, a single conventional LCoS panel cannot separate natural light or a white light source into primary color lights, the green light, red light, and blue light, or other color lights to produce images. Therefore, the above-mentioned color wheel or color separation and combination optical system have to be used with several LCoS panels for generating colorful images, thus a conventional LCoS display with pluralities of LCoS panels and a complex optical engine has high fabrication cost and does not meet the market requirement of small-size products.
The U.S. Pat. No. 4,534,620 provided by Gale et al. mentions that yellow, green, or cyan dichroic films might be stacked to form a color-encoding transmissive filter, wherein complicated processes, such as the adoption of both the dry and wet etching processes, have to be in cooperation with some specific materials, such as a surface material inert to wet etchants, for forming the predetermined profiles of the yellow, green, or cyan stacked structures because their etching selection ratios are very low. In addition, Jisaka further provides an U.S. Pat. No. 7,121,669 to disclose a fabrication method of a color pixel array of a transparent TFT-LCD. He teaches depositing a first layer of color filter on a transparent glass or quartz substrate, etching the color filter to define a predetermined pattern, forming a thick transmissive interlayer on the color filter, depositing a second layer of color filter on the transmissive interlayer, etching the second color filter, and forming another thick transmissive interlayer thereon. The above-mentioned processes may be repeated several times to form a color filter structure with a thickness comprising at least three color filters and three thick transmissive interlayers on the transparent substrate. Accordingly, the fabrication method of color pixel array disclosed by Jisaka is complicated and expensive, and his color filter structure is too thick to meet the small-size requirement of display market.
As a result, how to fabricate micro color filters with different colors or a color pixel array on a semiconductor substrate of a single LCoS panel through simple processes is still an important issue for LCoS display manufacturers.